This invention relates generally to friction clutches, and in particular to a clutch for transmitting increased power without any corresponding increase in size or weight.
Friction clutches are widely used in trucks and other automotive vehicles to selectively connect a driving shaft which is a source of rotational power, such as an engine crankshaft, to a driven shaft, such as a transmission input shaft. A typical clutch has a moveable pressure plate connected for rotation with the driving shaft and a friction disk connected for rotation with the driven shaft. When the pressure plate is moved to a position where it clamps the friction disk in engagement against a flywheel on the end of the driving shaft, the driven shaft rotates with the flywheel and torque is transmitted from the driving shaft to the driven shaft. When the pressure plate is moved to a position where the friction disk is disengaged from the flywheel, no torque is transmitted and a driver of the vehicle is free to shift gears of the transmission.
A release assembly is typically provided for moving the pressure plate into and out of position where the friction disk engages the flywheel. The release assembly includes a sleeve-shaped retainer hub which is moveable to actuate motion of the pressure plate. One or more levers are pivotally disposed between the retainer and the pressure plate, linking them together such that movement of the retainer causes a corresponding movement of the pressure plate. Compression springs are included which urge the retainer toward a position where the pressure plate clamps the friction disk against the flywheel, and which hold the pressure plate in its engaged position. The levers provide a mechanical advantage in that force applied by the springs is transmitted through the levers and its magnitude is multiplied by a lever ratio. Therefore, the force of the pressure plate against the flywheel, known as the plate load, is larger than the spring force. The release assembly also includes a foot pedal in the vehicle that is operatively connected to the retainer. When the driver of the vehicle presses upon the foot pedal, he or she opposes and overcomes the spring force in moving the retainer to a position where the friction disk disengages from the flywheel. The driver is then free to shift gears of the transmission. On subsequent release of the foot pedal, the spring force on the retainer and, through the levers, on the pressure plate, returns the retainer and pressure plate to their original positions wherein the friction disk engages the flywheel.
Recent trucks and other automotive vehicles include an engine of significantly greater horsepower and torque that requires a clutch which transmits more power. That clutch must provide a correspondingly greater plate load to hold its pressure plate in position to avoid slipping. To facilitate a larger plate load, some clutches include springs of increased number, size, or a different type which apply a larger force upon the retainer and thereby upon the pressure plate. Unfortunately, these springs detrimentally increase weight and volume of the clutch. Further, since the driver must oppose a larger spring force when pressing upon the foot pedal, the clutch is more difficult to operate. These clutches are complex, increase cost, and reduce reliability of the clutch.
Among the several objects and features of the present invention may be noted the provision of a clutch suitable for use in vehicles with higher torque engines; the provision of such a clutch that transmits larger forces without increasing size or weight of the clutch; the provision of such a clutch that minimizes force that must be applied to disengage the clutch; the provision of such a clutch which is reliable; and the provision of such a clutch that is economical.
A friction clutch of the present invention connects driving and driven shafts. In general, the clutch comprises a pressure plate adapted for operative attachment to the driven shaft for rotation therewith. The pressure plate is axially moveable between an engaged position wherein the pressure plate clamps a friction disk of the driven shaft in engagement against a flywheel of the driving shaft thereby to transmit torque from the driving shaft to the driven shaft and a disengaged position wherein the pressure plate does not clamp the friction disk and no torque is transmitted. A retainer is axially moveable and capable of operative connection to a foot pedal for selectively applying force to the retainer for axial movement thereof. A cover is adapted for mounting on the flywheel in stationary axial position relative to the flywheel. The cover includes an adjusting ring which is adjustably moveable in axial position. At least one spring is interposed between the cover and the retainer for urging the retainer to an axial location wherein the pressure plate is in the engaged position. The clutch includes at least one lever for actuating the axial movement of the pressure plate in response to axial movement of the retainer. The lever has a pivot fulcrum engaging the adjusting ring, a first bearing surface engaging the retainer for axial movement therewith and a second bearing surface engaging a face on the pressure plate for axially moving the pressure plate. The pivot fulcrum, first bearing surface, and second bearing surface are formed into the lever and arranged relative to each other such that a lever ratio of a first distance from the pivot fulcrum to the first bearing surface to a second distance from the pivot fulcrum to the second bearing surface is at least about 7.5 for augmenting an axial force applied by the spring to urge the pressure plate toward the engaged position.
In another aspect, a lever of the present invention is for inclusion in a friction clutch. The lever is configured to actuate axial movement of a pressure plate adapted for selectively clamping a friction disk against a flywheel of a driving shaft. The pressure plate is moveable between an engaged position wherein the friction disk engages the flywheel thereby to transmit torque from the driving shaft to the driven shaft and a disengaged position wherein the friction disk is disengaged from the flywheel and no torque is transmitted. The lever is configured for being pivotally disposed to transmit motion and force between an axially moveable retainer and the pressure plate. The lever comprises a onepiece plate formed to have a pivot fulcrum for engaging an adjusting ring of a clutch cover, a first bearing surface for engaging the retainer, and a second bearing surface for engaging the pressure plate. The pivot fulcrum is located a distance D1 from the first bearing surface. The pivot fulcrum and second bearing surface are constructed and arranged relative to each other so that the distance separating the pivot fulcrum from the second bearing surface is less than or equal to D1/7.5.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.